pcre32: Add 32-bit library
Create libpcre32 that operates on 32-bit characters (UTF-32).
This turned out to be surprisingly simple after the UTF-16 support
was introduced; mostly just extra ifdefs and adjusting and adding
some tests.

Refactoring to reduce stack usage for possessively quantified subpatterns. Also
fixed a number of bugs related to repeated subpatterns. Some further tidies
consequent on the removal of OP_OPT are also in this patch.

Applied Bob and Daniel's patches to convert the build system to automake. Added
the maintain directory, containing files that are used for maintenance, but are
not distributed. This is an intermediate step.